Perhaps one the most popular auxiliary languages ever invented, including, possibly, up to two million speakers, the highest ever for a constructed language and the only one to date to have its own native speakers (Approximately 1000).[citation needed]

Controlled languages are natural languages that have in some way been altered to make them simpler, easier to use, or more acceptable in certain circumstances, such as when a person does not speak the original language well. The following six projects are example of controlled English:

Basic English, Special English and Globish — seek to limit the language to a given list of common-use words and terms in order to make it simpler to foreign learners or other people who may have difficulties

Plain English — proposes a more direct, short, clear language by avoiding many idioms, jargon and foreign words

Resource Description Framework (RDF), a language standardized by the World Wide Web Consortium (W3C) based on the principles of Common Logic, which represents knowledge as a directed graph built from unordered sets of "sentences" (in fact, as relational triples: subject, relation, attribute) using various syntaxes (XML, Turtle, JSON-LD, RDFa) for its interchange format. Each element of the triple can be either a simple value (if its semantic value is not specified outside of the relation using it), or identifiers of objects (such as URIs) that are part of enumeration built from another subset of relational triples. The relations may be open (in which case the attributes are not enumerable) or closed in a finite enumerable set whose elements can be easily represented as objects as well with their own identity participating in many different relations for other parts of the knowledge.

UML may be used to describe the sets of relations and rules of inference and processing, and SQL may be used to use them in concrete schemas and compact store formats, but RDF designs its own (semantically more powerful) schema language for handling large sets of knowledge data stored in RDF format.

RDF is probably useful only for automated machine processing, but its verbosity and complex (for a human) representation mechanisms and inference rules does not qualify it as a human language except in very limited contexts. It is still a specification with extensive research.

Web Ontology Language (OWL), another knowledge representation language standardized by W3C, and derived from Common Logic.